Biocompatible medical articles and process for their production

ABSTRACT

An article of metal, glass, ceramics or plastics having a surface for contact with tissue or with circulating blood, has a surface coating of an organopolysiloxane and heparin, in which coating the organopolysiloxane is adherent to the surface of the article and has cationic groups that form ionic bonds with anionic groups of the heparin. The surface for contact with circulating blood may be an interior surface of a cannula or tubing or of a blood oxygenator or it may be a working surface of a blood filter. The polymer may be poly-[dimethylsiloxane-co-methyl-(3-hydroxypropyl)siloxane]-graft-poly(ethylene glycol) [3-(trimethylammonio) propyl chloride] ether. A method is also provided for forming a coated article as aforesaid, said method comprising contacting said surface with a solution in a volatile organic solvent of an organopolysiloxane and with heparin, the organopolysiloxane being adherent to the surface of the article and having cationic groups that form ionic bonds with the anionic groups of the heparin, and removing said volatile solvent.

FIELD OF THE INVENTION

[0001] This invention relates to medical articles that can be placed incontact with a stream of blood or other tissue and which have surfacesthat are anti-thrombogenic. It also relates to a process for treating amedical article to impart anti-thrombogenic properties to a surfacethereof.

BACKGROUND TO THE INVENTION

[0002] Articles for contact with circulating blood, whetherintra-corporeally or during extracorporeal blood circulation, can giverise to coagulation. In particular, plastics materials have been foundto be thrombogenic, even in the case of relatively blood-compatiblematerials such as polytetrafluoroethylene and silicone rubber. In orderto minimize trauma in blood circulating in contact with articles havingnon-biological surfaces, bonding of heparin to such surfaces has beendisclosed, the heparin imparting anti-thrombogenic properties.

[0003] Bonding of heparin to surfaces was first described by V. I. Gottet. Al., Science, 142, 1297 (1963), the surfaces being graphitized,treated with benzalkonium chloride and then with heparin. Subsequently asimpler surface treatment was developed based on coating the surfacee.g. by simple immersion with a thin layer of tridodecylmethyl ammoniumheparinate, see V. I. Gott et. al., Ann. Thoracic Surg., 14, 219 (1972)and A.H. Krause et. al, Ann. Thoracic Surg., 14, 123 (1972). Accordingto a data sheet issued by Polysciences Limited of Northampton, Englandin 1984 the process was used to make shunts for use in artery bypass.Greater stability to washing can be achieved by cross-linking the bondedheparin molecules with dialdehydes, see U.S. Pat. No. 3,810,781(Eriksson), and an increased level of heparin uptake can be achieved inthe case of plastics articles by glow-or corona-treating the surface ofthe article, see U.S. Pat. No. 4,613,517. The use of so-called “DurafloII heparin” coatings to reduce blood trauma in extracorporeal circuitse.g. of cardiopulmonary bypass machines is disclosed by Li-Chien Hsu,Cardiac Surgery: state of the art reviews-Vol. 7, No. 2, 265 (1993). Theeffectiveness of so-called “heparin bonded circuits” in reducing theneed for blood transfusion during coronary artery bypass surgery isdisclosed by G. M. Mahoney et. al., European Journal of Cardio-thoracicSurgery.

[0004] Various references disclose the treatment of surfaces withheparin and with a silicone. For example U.S. Pat. No. 4,529,614 (Burns)discloses the coating of microcontainer tubes for use in blood testingwith an aqueous solution of heparin and an organopolysiloxane to form ahydrophobic anticoagulant layer. U.S. Pat. No. 5,061,738 (Solomon et al)discloses a medical device such as a probe, cannula or catheter which isrendered both antithrombogenic and lubricious by treatment of a mixtureof a quaternary ammonium complex of heparin and a non-curing lubricatingsilicone which may be a polydialkylsiloxane. U.S. Pat. No. 5,182,317(Winters et. al.) discloses the production of multi-functionalthrombo-resistant coatings for use with biomedical devices and implants.A material is prepared which has a siloxane surface onto which aplurality of amine functional groups is bonded. Either the surface isplasma etched with ammonia gas or a siloxane monomer is plasmapolymerized in the presence of ammonia gas. The resulting siloxanesurface containing amine groups is reacted with poly(ethylene oxide)chains terminated with functional groups that can react with the aminegroups on the siloxane surface. The product is then further reacted withat least two different molecules that are capable of resisting bloodmaterial incompatibility reactions. U.S. Pat. No. 5,541,167 discloses adevice for removing air bubbles from blood (“defoaming”) before theblood is returned to a patient. Sequential coatings of a quaternaryammonium complex of heparin and of a mixture of a polysiloxane andsilicon dioxide are applied.

SUMMARY OF THE INVENTION

[0005] The present invention provides a polymeric coating that may beapplied to an article for surgery, diagnosis or other medical treatmentand in which heparin and/or or another negatively charged biologicallyactive molecule is simply and effectively bound to a substrate.

[0006] The substrate is treated with a polydimethylsiloxane-based primerwhich adheres firmly to the surface of the article without the need forpre-treatment (e.g. by plasma discharge or by a coupling agent) andwhich has exposed cationic sites. The primer forms a thin transparentlayer and is not detrimental to the mechanical properties of the device.Simultaneously or subsequently the heparin and/or other negativelycharged biologically active molecules are applied to the article.Treatment can be carried out at ambient temperatures. After treatmentthe article may be washed to remove solvent and un-reacted reagent anddried either with moderate heat insufficient for reduction of thebiological activity of the heparin to take place or at ambienttemperatures.

[0007] In one aspect the invention provides an article having a surfacefor contact with circulating blood, said surface having a coating of anorganopolysiloxane and heparin, wherein the organopolysiloxane isadherent to the surface of the article and has cationic groups that formionic bonds with anionic groups of the heparin.

[0008] In another aspect the invention provides an article having asurface for contact with circulating blood, said surface having acoating of an organopolysiloxane and a biologically active materialhaving anionic groups, wherein the organopolysiloxane is adherent to thesurface of the article and has cationic groups that form ionic bondswith anionic groups of the biologically active material. The anionicbiologically active molecule may, for example be a diagnostic agent,growth factor, antibody. prostaglandin (which can inhibit thrombusformation and platelet activity) or protein.

[0009] In a further aspect, the invention provides a method for forminga coated article as defined above, said method comprising:

[0010] contacting said surface with a solution in a volatile organicsolvent of an organopolysiloxane and with heparin, theorganopolysiloxane being adherent to the surface of the article andhaving cationic groups that form ionic bonds with the anionic groups ofthe heparin; and

[0011] removing said volatile solvent.

[0012] The surface of the article may be coated sequentially with theorganopolysiloxane and with heparin, or a complex of theorganopolysiloxane and heparin may be formed in solution, after whichthe solution is contacted with the surface of the article. The processmay be applied to the coating of other negatively charged biologicallyactive molecules in addition to or as an alternative to coating withheparin.

[0013] Use of the article in the recirculation of blood e.g. as a bloodline, oxygenator, heat exchanger, haemodyalyser and/or blood filter isalso within the scope of the invention. When heparin treated oxygenatorsor haemodyalysers are used, the dose of heparin that has to beadministered to the patient to enable the treatment to be conductedsafely can be reduced.

Description of Preferred Features

[0014] The article to be rendered bio-compatible may be at least partlyof a metal, ceramics or glass. It may also be at least partly of apolymeric material, e.g. polyethylene, polyacrylic, polypropylene,polyvinyl chloride, polyamide, polyurethane, polyvinyl pyrrolidone,polyvinyl alcohol, polystyrene, polysulfone, polytetrafluoroethylene,polyester, silicone rubber, natural rubber, polycarbonate or a hydrogel.The invention is particularly advantageous for the treatment of hollowarticles in which the surface for contact with circulating blood is aninterior surface, e.g. a cannula or tubing, a blood oxygenator (whichmay be provided with a reservoir and heat exchanger) or blood filter orhaemodyalyser.

[0015] The organopolysiloxane is preferably soluble in a lower alcohol,of which 2-propanol is preferred because of its combination ofvolatility and antiseptic properties. It preferably hastrimethylammonium groups linked to a polydimethylsiloxane main chain bygrafted polyoxyethylene chains, which preferably include hydroxylterminated chains, and quaternary ammonium terminated chains. Aparticular preferred cationic solvent-soluble silicone polymer used ispoly-[dimethylsiloxane-co-methyl-(3-hydroxypropyl)siloxane]-graft-poly(ethyleneglycol) [3-(trimethylammonio) propyl chloride] ether whose structure isbelieved to be generally as indicated below:

(CH₃)₃SiO[(CH₃)₂SiO]_(x)[(CH₃) (RO(CH₂ CH₂O)y CH₂ CH₂CH₂)SiO]_(z)OSi(CH₃)₃  (1)

[0016] wherein x, y and z represent integers and R, whose value maydiffer in different units along the chain, represents H or -[CH₂ CH₂CH₂N⁺(CH₃)₃] X wherein X represents chloride or another cation. Thematerial used may typically have a molecular mass of about 4000 andabout 4 quaternary ammonium groups per molecule.

[0017] The organopolysiloxane may be contacted with the surface of thearticle whilst it is in solution in an alcohol or aqueous alcohol e.g.2-propanol. Contact may be at ambient temperatures, and in the case of ahollow article it can simply involve circulation of the solution throughthe article to permit the organopolysiloxane to form a layer on thesurface to be treated. If the ionic complex is not preformed, theheparin or other biologically active material may be applied as anaqueous solution at ambient temperatures, so that the proceduresinvolved are relatively rapid and inexpensive. In the case of anaqueous/alcohol mixture, the alcohol should predominate, a ratio of 1:10helping to solubilize hydrophilic materials whilst preserving theantiseptic qualities of the alcohol. Where the surface to be treated isone face of a membrane or tube of microporous material (e.g. microporouspolypropylene or polysulfone fibers), gas under pressure is preferablysupplied to the other face of the membrane or tube to keep the poresopen.

[0018] The process has been applied successfully to medical devices suchas oxygenators, blood filters, and PVC tubing used in glucose monitoringsystems, and the coated articles have been successfully tested forbiocompatibility. The process has also been applied to haemodyalysers,and both the case and the fibrous membranes of a haemodyalyser have beensuccessfully coated. Our experiment was carried out with a haemodyalyserhaving microporous polysulfone membranes and a polycarbonate case.

[0019] The invention will now be further described, by way of exampleonly with reference to the following examples:

EXAMPLE I Treatment of a Hollow Fiber Oxygenator

[0020] Experiments were carried out to determine conditions for thetreatment of a hollow fiber blood oxygenator. Such an oxygenator is asingle use device, which is used for oxygenating blood during cardiacsurgery. Blood is diverted from the right atrium and pumped along tubingby means of a peristaltic pump into a reservoir, which gives theperfusionist a volume of blood on which to work. The blood is thendirected from the reservoir to a heat exchanger compartment of theoxygenator, where it can be heated or cooled according to demand bywater flowing through heat exchanger tubes of polyethylene or stainlesssteel. Blood proceeds from the heat exchanger into an oxygenatorcompartment where oxygen is introduced into the blood by contact withthe surfaces of hollow fibrous tubes of microporous plastics materiale.g. polypropylene. The use of fibers is not critical and otheroxygenators use membranes e.g. of silicone. Blood is returned to thepatient via the aorta. The use of a cardiopulmonary bypass circuitincluding a heat exchanger and oxygenator unit of the above kind allowsthe surgeon to cool the heart to reduce its oxygen demand and then stopthe heart beating for a period of time while he is working on the heart.The use of such a by-pass also allows all the blood to be drained fromthe veins and arteries of the heart.

[0021] An object of the present experiment was to find a way ofimproving the biocompatibility of the internal surfaces of thereservoir, heat exchange compartment and oxygenator compartment andproviding them with a surface layer which was non-thrombogenic.

[0022] A 1% solution of the polymer (I) in 2-propanol (fromSigma-Aldrich company Ltd, Poole, Dorset) was circulated through anoxygenator assembly as described above for a period of 15 minutes and ata rate of 0.7 liters/minute. Oxygen at a positive pressure of 0.1atmosphere was supplied to the “O₂ in” line to prevent liquid enteringthe gas side of the oxygenator and to keep the pores of the hollowfibres open and so maintain the oxygen-permeability of the device. Afterthe circulation step had been completed, excess 2-propanol solution wasblown out of the oxygenator with gas from the oxygen line. The apparatuswas then rinsed with deionized water, the de-ionized water was blown outusing oxygen gas, and the apparatus was dried in an oven at 50° C.overnight. The various internal surfaces of the assembly were thentested with Eosin Y. A red stain developed at each surface, which wastaken as an indication that the polymer (I) had become attached.

[0023] A second oxygenator assembly was treated as indicated above,after which a 0.1% solution of heparin (Celsus) in de-ionized water wascirculated for about 5 hours, again with a positive pressure of oxygenin the “O₂ in” line. The oxygen line was then used to blow excessheparin solution out of the assembly. The apparatus was then againwashed with de-ionized water, the de-ionized water was blown out usingoxygen gas, and the assembly was oven-dried at 50° C. overnight. Theinternal surfaces of the assembly were contacted with toluidene blue. Adark purple stain developed on the fibers within the oxygenator, andalso on the walls of the oxygenator which were of polycarbonate. Thiswas taken as an indication that the heparin had become ionically bondedto the previously formed internal coating of polymer (I).

[0024] Blood (about 500 ml) from an abattoir was treated with a solutionof heparin (0.2 g) in saline (0.9%; 50 ml) to allow it to be transportedto the laboratory without coagulation. Protamine sulfate was added tothe fully heparinized blood to reduce the ACT (activated clotting time)to about 200-400 sec which is comparable to that of untreated freshblood. The following procedure was adopted to determine the amount ofprotamine sulfate to be added. A solution of protamine sulfate (0.1 g)was prepared. A sample of the blood was steadily agitated and 20 ml wasintroduced into a plastics container, followed by about 200 {grave over(┐)} of the protamine sulfate solution. Two ml of the resulting solutionwere withdrawn and placed into a flip top tube of a Haemochron wholeblood coagulation system. The tube was placed into a Haemochron 401coagulation detector that measures the length of time that the bloodtakes to clot (ACT). The volumes of the protamine sulfate solution wasvaried as required to bring the measured ACT within the 200-400 secrange set out above. Then protamine sulfate was then added to theremainder of the 500 ml of fully heparinised blood in the ratioindicated by the preceding test.

[0025] The heparinised and protamine sulfate treated blood was thencirculated through an oxygenator treated with the polymer (I) alone, andthrough an oxygenator treated with both the polymer (I) and withheparin. In the former case, the blood clotted immediately, whereas inthe second case the measured ACT was above 1500 seconds which was muchmore that of the blood at the start of the experiment. This was taken toindicate that heparin was being released from the coated internalsurface of the apparatus and was effective to inhibit clotting.

[0026] Oxygenators treated as described above were found to passcytotoxicity and haemolysis tests by a wide margin.

EXAMPLE 2

[0027] A 0.1 wt % solution of polymer (I) in 2-propanol was circulatedthrough an oxygenator assembly as described in Example I at 80 ml/minutefor 30 minutes, during which time air from a compressor was supplied tothe “O₂ in” line. Excess polymer (I) solution was then flushed out withoxygen, after which the oxygenator was dried at 50° C. for about 7 hourswith air from the compressor being supplied to both the “O₂ in” line andthe “blood in” line. De-ionized water was then circulated through theoxygenator at a rate of 80 ml/min for about 1 hour, during which timeair from the compressor was supplied to the “O₂ in” line.

[0028] A 0.1 wt % solution of heparin in de-ionized water was thencirculated through the oxygenator for about 1 hour at a rate of 80ml/min, during which time air from the compressor was supplied to the“O₂ in” line. De-ionized water was then circulated through theoxygenator for about 1 hour at 80 ml/min while air from the compressorcontinued to be supplied to the “O₂ in” line. Oxygen was then blownthrough the oxygenator to flush out most of the de-ionized water, afterwhich the oxygenator was dried at room temperature (to avoid thermalreduction of the heparin bioactivity) for 12.5 hours, with thecompressor supplying air to the “O₂ in” line and to the “blood in” line.The oxygenator was then ready for use.

[0029] An oxygenator treated as indicated above was found to have agenerally constant ACT over a blood circulation period of 7 hours and tobe free from leakage of blood into the “O₂ in” line.

EXAMPLE 3

[0030] A solution of polymer (I) (0.88 g) in 2-propanol (350 g) wasmixed with a solution of heparin (0.05 g) in de-ionized water (50 g).Mixing was continued for 15 minutes, after which the mixture wascirculated through an oxygenator as described in the preceding examplesfor a period of 30 minutes, during which time air from the compressorwas supplied to the “O₂ in” line. De-ionized water was then circulatedthrough the oxygenator for about 1 hour at 80 ml/min while air from thecompressor continued to be supplied to the “O₂ in” line. Oxygen was thenblown through the oxygenator to flush out most of the de-ionized water,after which the oxygenator was dried at room temperature for 6 hours toavoid thermal degradation of the heparin, with the compressor supplyingair to the “O₂ in” line and to the “blood in” line. The working surfacesof the oxygenator were tested with toluidine blue and a dark purplestain developed. This was taken as an indication that the heparin hadbecome ionically bonded to the polymer (I) which had during thesubsequent circulation step formed a coating on the working surfaces ofthe oxygenator.

EXAMPLE 4 Animal Trial

[0031] Several components of Extracorporeal products such as Safe Minioxygenators, reservoirs and silicone tubes were coated with polymer (I)and then coupled with heparin using the method described in example 2.

[0032] The heparin coated oxygenators, reservoir and silicone tubes werethen used for in-vivo test with a pig model and compared with uncoatedcircuit. The objective was to show the difference between heparin coatedand uncoated product during in-vivo test of an Extracorporealcirculation (ECC) at a reduced ACT level over the time of the test dueto the body metabolism of the animal. The tests were carried out inparallel using either two or four Safe Mini Oxygenators for each run.The design of this test is to make sure that the coated and uncoatedproducts can be compared under identical conditions. The initial levelsof ACT was approximately 480 seconds, which is normally recommended withECC. After 2-3 hours of circulation, the ACT level was in the region of125-200 seconds.

[0033] During this test the products were examined for the presence ofany clotting and photographs were taken at the end of the test. Allproducts were then flushed with saline and inspected for clotting or anyother blood deposition.

[0034] Results:

[0035] (1) It was clearly observed that micro clots deposited on all sixuncoated products especially when the ACT reached to 250 seconds. Theamount and the size of the clot were also increased when the ACT wasdecreased further at the advancing time of the test.

[0036] (2) On the other hand no visible clots were seen onto the sixheparin coated products.

[0037] (3) No significant increase in pressure drop was observed, exceptin the first pair of products, where the pressure drop increased 20 mmHgin total for the coated one and 72 mmHg for the uncoated products.

[0038] (4) Significant amounts of clots were observed onto the surfaceof the uncoated products after flushing the blood with slain.

[0039] (5) No signs of clots onto the surface of heparin coated productswere shown after flushing the blood with slain. Few blood depositionswere seen in some areas of these products which are insignificantcompare to the uncoated products.

1. An article having a surface for contact with circulating blood, saidsurface having a coating of an organopolysiloxane and heparin, whereinthe organopolysiloxane is adherent to the surface of the article and hascationic groups that form ionic bonds with anionic groups of theheparin.
 2. The article of claim 1, which is at least partly of a metal,ceramic or glass.
 3. The article of claim 1 or 2, which is at leastpartly of a polymeric material.
 4. The article of claim 3, wherein thearticle is of polyethylene, polyacrylic, polypropylene, polyvinylchloride, polyamide, polyurethane, polyvinyl pyrrolidone, polyvinylalcohol, polystyrene, polytetrafluoroethylene, polyester, siliconerubber, natural rubber, polycarbonate or a hydrogel.
 5. The article ofany preceding claim which is hollow and in which the surface for contactwith circulating blood is an interior surface.
 6. The article of anypreceding claim, which is a cannula or tubing.
 7. The article of any ofclaims 1-5, which is a blood oxygenator, blood filter or haemodyalyser.8. The article of any preceding claim, wherein the organopolysiloxane isadherent without a coupling agent.
 9. The article of any precedingclaim, wherein the organopolysiloxane is soluble in an alcohol.
 10. Thearticle of any preceding claim, wherein the organopolysiloxane hastrimethylammonium groups.
 11. The article of any preceding claim,wherein the organopolysiloxane has cationic groups linked to apolydimethylsiloxane main chain by grafted polyoxyethylene chains. 12.The article of claim 11, wherein the grafted polyoxyethylene chainsinclude hydroxyl terminated chains and quaternary ammonium terminatedchains.
 13. The article of any preceding claim, wherein the polymer ispoly-[dimethylsiloxco-methyl-(3-hydroxypropyl)siloxane]-graft-poly(ethyleneglycol) [3-(trimethylammonio) propyl chloride] ether.
 14. A method forforming a coated article as defined in any preceding claim, said methodcomprising contacting said surface with a solution in a volatile organicsolvent of an organopolysiloxane and with heparin, theorganopolysiloxane being adherent to the surface of the article andhaving cationic groups that form ionic bonds with the anionic groups ofthe heparin, and removing said volatile solvent.
 15. The method of claim14, wherein the surface of the article is coated sequentially with theorganopolysiloxane and with heparin.
 16. The method of claim 14, whereina complex of the organopolysiloxane and alcohol is formed in solutionand the solution is contacted with the surface of the article.
 17. Themethod of claim 14, 15 or 16, wherein organopolysiloxane is contactedwith the surface of the article whilst in solution in an alcohol. 18.The method of claim 17, wherein the alcohol is 2-propanol.
 19. Themethod of any of claims 14-18, wherein the surface to be treated is oneface of a membrane or tube of microporous material, gas under pressurebeing supplied to the other face of the membrane or tube.
 20. An articlehaving a surface for contact with circulating blood, said surface havinga coating of an organopolysiloxane and a biologically active materialhaving anionic groups, wherein the organopolysiloxane is adherent to thesurface of the article and has cationic groups that form ionic bondswith anionic groups of the biologically active material.
 21. The articleof claim 20, wherein the biologically active molecule is a diagnosticagent, growth factor, or antibody, prostaglandin or protein.
 22. Use ofan article according to any of claims 1-13 in the re-circulation ofblood.
 23. A method for forming a coated article substantially asdescribed in any of the examples.